Dangers Of The Deep

We know how dangerous the oceans are with their fierce winds, violent waves and treacherous currents, but when we are anchoring in clear, shallow waters, wading ashore from a dinghy, clambering over partly submerged rocks, or taking a cooling swim, we tend to feel quite safe. Not so! There are some dangerous creatures lurking just below the surface to take us unawares. Take a look at an A – Z of some of the most deadly.

Alligators and Crocodiles

Lurking just below the surface in marshes and lakes in the tropics, they pose a threat to divers or people in small boats, such as canoes. Crocs in particular are very territorial and can move extremely fast for their weight. They have been known to attack fully-grown buffalos and even sharks, pulling their victims down into the water and drowning them before they are devoured.


A large ray-finned, carnivorous fish measuring up to 7 feet and found in large schools in tropical and subtropical oceans, it is found near the surface of the water and near coral reefs and sea grasses. It doesn’t feed on humans but has been known to accidentally attack people wearing brightly coloured items such as watches, necklaces or dive lights and may mistake snorkellers for large predators, tearing off chunks of flesh.


Belying its cute, whiskery appearance, this is a dangerous creature if provoked. When threatened it raises three barbed spines from its back and side fins, containing debilitating venom which can cause severe pain, although it is not usually deadly. Even in refrigerated specimens the venom remains active for several days, so they must be handled with care. They rarely attack humans but there have been a few cases over the years when attacks proved fatal.

Crown of Thorns Starfish

This is a carnivorous predator measuring up to 60cm in diameter with 13 to 16 arms covered with sharp spines or thorns and a crown shape which gives it its name. Living around coral reefs, it releases digestive enzymes to liquefy the coral tissue and it can consume six square meters of coral per year. The thorns can pierce through clothes or wetsuits causing severe pain, possible bleeding, nausea, vomiting and inflammation which may continue for weeks or months if the spines are left in the wound.

Fire Coral

Often mistaken for coral or seaweed, with its brown or yellowy-green colour, Fire Coral is a type of marine organism living in large colonies and closely related to jellyfish and anemones. It can deliver a powerful sting with its invisible tentacles, causing anything from mild irritation to severe pains, nausea or vomiting. It is fairly common and should be handled carefully.

Jelly Fish

The Box Jellyfish is found in the warm waters of the Pacific and Indian Oceans and sometimes referred to as the Box of Death (an apt title). It is one of the most deadly sea-creatures; frequenting many popular beaches but hard to spot because of its translucent body. It can have up to 60 tentacles which may measure up to 5 metres in length and have around 5,000 stinging cells. It is one of the largest jellyfish but its relative fragility means that its venom has to be very strong, able to kill an aggressor at first contact. It has been known to kill a victim within 4 minutes, even faster than a snake. A fully grown adult needs to come into contact with only 3 tentacles to risk death and even if he is lucky, the sting will be so excruciating that the body may go into shock and the victim may drown. Immediate treatment should be the application of vinegar, followed by medical attention and CPR may also be required. There is no anti-venom so it is important to seek help quickly.

Most of the common jellyfish don’t seem to cause too many problems but the Portuguese Man-o-War, often encountered off the Spanish coastline, can spark heart attacks or death in those allergic to their poison. The best remedy for a mild sting seems to be removing any tentacles with tweezers and applying white vinegar, but severe reactions need hospital treatment.

Lion Fish

Found in the Caribbean and Eastern Atlantic, it is one of the most beautiful fish in the oceans with its showy pectoral fins and venomous spiky tentacles. It is a predatory fish with venom causing vomiting, fever, sweating and even death in some cases. Lionfish do not usually attack humans unless provoked, but once stung the victim should soak the injured part in hot water and seek medical attention.

Moray Eels

At 6 to 8 feet in length, with razor sharp teeth, they are scary looking creatures, but although their bites can lead to profuse bleeding and bacterial infection, these eels are not usually aggressive toward humans. They tend to hide in rocky cracks and crevices during the day and hunt at night. They do tend to be territorial, so should be approached with care.

Octopus, Blue-ringed

This small octopus, no more than 20 cm across, is found in shallow waters and tidal pools in tropical areas. The blue rings can change in intensity according to its mood and although its bite is not particularly painful the effects can be catastrophic, causing paralysis and death within a very short time by injecting a neuromuscular paralizing venom. There is no known antidote but there are instances where victims have survived by being put on a respirator before cyanosis and hypotention develops.

Puffer Fish

With their ability to suddenly bloat and puff themselves up, one might be lured into thinking them cute and harmless. Don’t be mislead! These appealing looking creatures carry tetrodoxotin (TTX), a deadly poison more dangerous than cyanide. Not all puffer fish carry these toxins, however, and many are even eaten in Japan.

Sea Lions

Often thought of as gentle giants and frequently showing playful behaviour, they can be territorial and dangerous especially during the mating seasons. Accidents among divers are reported as being more frequent than with sharks. If you hear their territorial barking call, then keep well away.

Sea Snakes

Found in the warm waters of the Indian and Pacific Oceans, they resemble a cross between a land snake and an eel. A Sea Snake, unlike eels, does not have gills and needs to return to the surface for air. It often grows 2 to 5 feet in length but some species can reach lengths of 10 feet. There are 87 species and are not normally aggressive, but some carry extremely toxic venom. The Pelamis Platrus can be fatal to humans, so while attacks are rare these creatures should not be messed with. Their poison is 20 times more powerful than a cobra’s, but they inject much less of it. If you are unfortunate enough to be a victim, immediate action should be immobilization and pressure bandaging, followed by medical treatment, which may include CPR and administration of antivenom, as there may be danger of cardiovascular failure and renal problems.

Sea Urchin

It is so easy to step onto a spiny sea urchin. The long, sharp spines can penetrate very deep and break off, causing severe pain and infection. Sometimes they need to be removed surgically. I remember spending several hours trying to remove spines from my husband’s foot with a pair of tweezers, after first anaesthetizing him with copious amounts of alcohol. Not all Sea Urchins are venomous but one of the most deadly is the Flower Urchin, covered with flowers instead or thorns. This can cause paralysis or even death.

Sea Worms

There are many species of tropical sea worms lurking in coral or under rocks. While they are not dangerous, they can produce painful itchy rashes which can last for hours. They are best treated with antihistamine or steroid cream.


Thanks to reports in the media and films, we tend to think of sharks as the ultimate marine killers. In fact sharks don’t usually attack unless provoked and most of the attacks on humans have probably happened when they have mistaken the swimmers for the marine creatures on which they prey. Of the 350 species of sharks only 30 could potentially be dangerous to humans and only 12 are reported as being aggressive. Among the most dangerous to humans are the Great White, the Tiger Shark, the Bull Shark, the Ocean White Tip, the Gray Shark and the Mako. There are around 300 times more drowning accidents reported than fatal shark attacks, but the best way to avoid shark attack is to stay away from shallow waters where they are know to be feeding and don’t ignore warnings that they are in the vicinity. If you are confronted with a shark they may shy away from someone brandishing a stick or long object and their weak points are their gills, so striking them here could fend them off. Better still – don’t put yourself in that position!


Surprisingly various types of sponges can produce irritations and pain for quite long periods. It is safest not to touch any sponge, even dead ones washed onto the shore.


These creatures actually kill a lot more people than sharks. While they are not aggressive animals and often flee when attacked, they do object to being stepped on and use their tail stinger as a whip. Most attacks are not serious, although they can be extremely painful and some can be fatal, as Steve Irwin, the “Crocodile Hunter”, found out. As they lie on or near the bottom, often submerged in the sand, the safest way to act is to keep your feet off the bottom while diving or swimming, or shuffle your feet when wading in shallow water instead of stepping out.


A master of camouflage, it can be found on the sea bottom, mainly in the Indo-Pacific oceans, where it disguises itself as a rock. In spite of its small size, (up to 12 inches), it is the most poisonous fish in the world, having 13 spikes on its back filled with extremely potent, protein-based venom, which has the ability to kill a person in a few hours unless they receive medical attention. The sting causes excruciating pain, shock and paralysis and survivors have been known to suffer permanent nerve damage. First aid involves removing pieces of spines, encouraging bleeding to remove some of the venom, washing and soaking with water (preferably hot), then rest, elevate and dress with something clean. Medical advice should be sought as soon as possible and an injection will probably be given.


Large squids have been reported to be extremely aggressive, sometimes injuring fishermen. Some Giant Squids, living thousands of feet deep in the ocean, have even been believed to attack large boats.

Surgeon fish

This beautiful tropical fish is characterized by the scalpel-like spine protruding from the junction of its body and tail, which can be venomous in some species. Injuries only usually happen when the fish are handled, but they can also cause ciguatera poisoning if eaten.

Weever Fish

They burrow themselves into the sand and trap passing fish as they swim by. Unfortunately their nasty poisonous spines are also a danger to swimmers and even people paddling in shallow water. The pain can be intense and feet can swell up badly and become numb. The remedy is to soak the wound in water as hot as can be tolerated as this neutralizes the poison.

It would be foolish to avoid venturing into the sea for fear of encountering these “nasties”. Many of their stings and attacks can be avoided by taking a few precautions; wearing diving boots or similar, and gloves if you are handling poisonous creatures and being receptive to any advice given by locals, fishermen and others who know the area. If you are stung or bitten, don’t delay in seeking medical advice. Finally take time to enjoy the wonderful variety of sea life just under the surface.

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